Oscillating phased-array ultrasound imaging catheter system

ABSTRACT

A dynamic ultrasound image catheter includes a catheter body with an acoustic window on the distal end, an ultrasound phased array transducer assembly configured to rotate within the acoustic window through an angle of rotation, an acoustic coupling fluid filling a gap between the transducer array and the acoustic window, and a drive motor at the proximal end of the catheter body that is configured to rotate the transducer array. The drive motor may transmit a rotational force to the ultrasound phased array transducer by a drive wire or by tension wires coupled to drive spools. A system processor coupled to the drive motor controls rotation of the transducer array and estimates the angular orientation of the transducer array. By taking ultrasound images at increments through the angle of rotation, the dynamic ultrasound image catheter can obtain images spanning a volume which can be processed to generate three-dimensional composite images.

FIELD OF THE INVENTION

The present invention relates to medical diagnostic systems and methods,and more particularly to ultrasound imaging catheter systems with arotating phased-array transducer.

BACKGROUND OF THE INVENTION

Recent advancements in miniaturization of ultrasound technology hasenabled the commercialization of catheters including phased arrayultrasound imaging transducers small enough to be positioned within apatient's body via intravenous cannulation. By imaging vessels andorgans, including the heart, from the inside, such miniature ultrasoundtransducers have enabled physicians to obtain diagnostic imagesavailable by no other means.

The diameter of catheters, particularly intracardiac catheters, arenecessarily restricted to about 10 French or smaller by the diameter andprofile of blood vessels through which the catheter may be advanced.Consequently, catheter-born ultrasound transducers have been restrictedto single transducer elements (providing only distance information) andlinear phased-array transducer assemblies which provide atwo-dimensional image.

SUMMARY OF THE INVENTION

The present invention is directed toward providing compact, portableultrasound systems which can generate images suitable for renderingthree-dimensional images of organs—particularly in connection withintra-body, percutaneous ultrasound probes, such as catheters andendoscopes containing ultrasound transducer arrays.

The embodiments of the present invention describe an imaging catheterwhich includes a stepper motor to allow the physician to generate anazimuthally rotation of the imaging elements about the catheter axiswhile producing a 3D image of the adjacent tissue.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and constitutepart of this specification, illustrate exemplary embodiments of theinvention, and, together with the general description given above andthe detailed description given below, serve to explain features of theinvention.

FIG. 1 is an illustration of a prior art intracardiac linearphased-array ultrasound imaging catheter.

FIG. 2 is an illustration of a portion of the prior art ultrasoundimaging catheter shown in FIG. 1.

FIG. 3 is a cross sectional view of an embodiment of a dynamicultrasound imaging catheter.

FIGS. 4A and 4B are longitudinal cross sectional views of twoembodiments of the distal end of the ultrasound imaging catheter shownin FIG. 3.

FIGS. 4C-4E are transverse cross sectional views of alternativeembodiments of the distal end of the ultrasound imaging catheter shownin FIG. 3.

FIGS. 5A and 5B are perspective views of an embodiment of a bearingassembly suitable for use in the dynamic ultrasound imaging cathetershown in FIG. 3 shown in FIG. 3

FIGS. 6A and 6B are cross sectional view of two alternative embodimentsof the distal end of the dynamic ultrasound imaging catheter.

FIGS. 7A-7C are perspective views of details of the alternativeembodiments illustrated in FIGS. 6A and 6B.

FIG. 8 is a cross section view of a portion of the detail illustrated inFIG. 7.

FIG. 9 is a cross section view of the distal tip of the dynamicultrasound imaging catheter showing an example implementation detail.

FIGS. 10A-10E are cross sectional views of alternative embodiments ofthe distal end of the dynamic ultrasound imaging catheter.

FIGS. 11A-11E are cross sectional views of alternative embodiments ofthe drive motor portion of the handle of the dynamic ultrasound imagingcatheter.

FIGS. 12A-12C are cross sectional views of details of alternativeembodiments of the distal end of the dynamic ultrasound imagingcatheter.

FIG. 13 is circuit block diagram of an embodiment of power and controlcircuits for the embodiment illustrated in FIG. 3.

FIG. 14 is a block/flow diagram of a method for controlling theoperation of the transducer array according to an embodiment.

FIG. 15 is a flow diagram of a method for determining the rotationalorientation of the transducer array according to an embodiment.

FIG. 16 is a flow diagram of a method for assembling an embodiment ofthe dynamic ultrasound imaging catheter.

FIG. 17 is a flow diagram of a method of using an embodiment of thedynamic ultrasound imaging catheter.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Various embodiments of the present invention will be described in detailwith reference to the accompanying drawings. Wherever possible, the samereference numbers will be used throughout the drawings to refer to thesame or like parts.

As used herein, the terms “about” or “approximately” for any numericalvalues or ranges indicate suitable dimensional tolerances that allow thepart or collection of components to function for their intended purposesas described herein. Also, as used herein, the terms “patient”, “host”,and “subject” refer to any human or animal subject and are not intendedto limit the systems or methods to human use. Further, embodiments ofthe invention will be described for use with an intracardiac ultrasoundtransducer array catheter; however, the embodiments may be applicable toany medical ultrasound transducer.

Phased array ultrasound imaging catheter systems, particularlyintracardiac ultrasound imaging catheters, generate two dimensionalsliced images of tissue within the field of view of the transducerarray. The ultrasound imaging catheter is limited to a small diameter,such as 6 to 10 French, so that it can be inserted into most organs ofthe body via catheterization through a vein or artery, or through smallincisions such as in an arthroscopic procedure. For example, anintracardiac ultrasound catheter can be introduced into the heartthrough the vena cava to image the atria and ventricles from justoutside or within the heart itself. Such access of the imaging sensorprovides image details and perspective that are available by no otherimaging means.

A conventional ultrasound imaging catheter system is shown in FIG. 1.Such systems include an imaging probe 120 electrically coupled to anisolation box 130 which is coupled to an ultrasound equipment 150 via acable 140. The imaging probe 120 includes a catheter 118 and transducerassembly 112 as shown in FIG. 1. The catheter assembly 112 includes anelongated catheter 118 generally in the form of a tube. The proximal endof the catheter 118 is connected to a handle mechanism 120 which caninclude mechanisms for controlling the steering of the ultrasound probe122 mounted at the distal end of the catheter 118.

The ultrasound probe 122, shown in more detail in FIG. 2, includes anultrasound transducer assembly 124, which is comprised of a number ofultrasonic transducer elements 126 having wires connected thereto whichare provided inside the catheter 118. Although only twelve or sotransducer elements 126 are shown in FIG. 2, typical ultrasoundtransducer arrays include 64 transducer elements 126 and substantiallyany number of transducer elements may be employed as described in theprior application discussed above. Mounted near the distal end, such ason the reverse side of the ultrasound transducer probe 122 is athermistor 128, which may be embedded within the probe 122. Thethermistor 28 is positioned so as to be able to sense the temperature ofthe tissue in the vicinity of the probe 122 and/or the temperature ofthe probe 122 itself. Examples of phased array ultrasound imagingcatheters used for intracardiac echocardiography and methods of usingsuch devices in cardiac diagnosis are disclosed in the following U.S.Patent Application Publications—each of which is incorporated herein byreference in their entirety.

-   -   2004/0127798 to Dala-Krishna et al.;    -   2005/0228290 to Borovsky et al.; and    -   2005/0245822 to Dala-Krishna et al.        Commercially available ultrasound catheters are available from        EP MedSystems, Inc. of West Berlin, N.J.

Electrical wires connected to the ultrasonic transducer elements 126 andthe thermistor 128 pass through the inside of the catheter body 118 andare connected by a cable 132 to an isolation box 130 which passes theelectrical signals to ultrasonic equipment 150 which operate in mannerswell known in the art.

The ultrasonic transducer elements 126 convert the electrical signalsfrom the ultrasound equipment 150 into high frequency sound waves whichpropagate into a portion of a patient's anatomy, such as the heart. Thesame ultrasonic transducer elements 126 also receive ultrasound echoesreflected from anatomic structures and transform the received sound intoelectrical signals (e.g., by means of the piezoelectric effect). Theseelectrical signals are conducted via cable 132 back to the isolation box130 and then to the ultrasound equipment 150.

Within the ultrasound equipment 150, a signal generator generateselectrical signals of ultrasonic frequencies which provided to theultrasonic transducer elements 126. The signal generator producessignals of particular wave forms, frequencies and amplitudes as desiredfor imaging tissue. Beam former circuits within the ultrasound equipment150 process signals sent to and received from the ultrasonic transducerelements 126 to enable phased-array ultrasound imaging. The beam formercircuits may receive ultrasound signals from the signal generator andintroduce phase lags for each ultrasonic transducer element 126 so thatwhen the signals are applied to the transducer elements a narrow beam ofsound emanates from the array due to constructive and destructive waveinteractions as well known in the art of imaging ultrasound phased arraytransducers. Also, the beam former may receive signals from thetransducer array and process the ultrasound echo signal data tocalculate the amplitude and direction of the ultrasound echoes returnedto the transducer elements 126 from each of many specific angles anddistances. The beam former circuits may also determine the frequency orDoppler frequency shift of the signal returned form each of selectedangles and distances from the transducer elements 126.

The isolation box 130 contains isolation circuitry which isolatesunintended, potentially unsafe electrical currents and voltages from thecatheter which contacts the patient. Examples of suitable isolationcircuits are described in U.S. patent application Ser. No. 10/997,898“Method And Apparatus For Isolating A Catheter Interface”, published asU.S. Patent Publication No. 2005/0124898 to Borovsky et al filed on Nov.29, 2004, the entire contents of which are hereby incorporated byreference. An example of such safety methods and systems is embodied inthe ViewMate® catheter ultrasound system from EP MedSystems, Inc. ofWest Berlin, N.J.

The circuits and functionality of the isolation box 130 and ultrasoundsystem 150 may be combined into a single unitary system as recentlydisclosed in U.S. patent application Ser. No. 11/610,778 entitled“Integrated Beam Former and Isolation For An Ultrasound Probe” and Ser.No. 11/610,866 entitled “External and Internal Ultrasound ImagingSystem,” both filed Dec. 14, 2006 and both of which are incorporatedherein by reference in their entirety.

Information obtained from the ultrasound transducer elements 126 isprocessed by the ultrasound equipment 150 to generate images which canbe stored and displayed on a monitor for review by a clinician. Theultrasound equipment 150 will generally include a programmableprocessor, such as a workstation computer, operating software forcontrolling the operation of beam former circuits and receiving andprocessing ultrasound data to generate ultrasound images. The operatingsoftware will also include user-interface modules for presenting a menuof control options and implementing user inputs. The ultrasoundequipment 150 may also a display for presenting ultrasound images to theuser, and user input devices, such as a keyboard and pointing device(mouse, light pen and/or touch screen display) for receiving usercommands and inputs. Ultrasound processors and software modules are wellknown in the intracardiac ultrasound imaging arts, an example of whichis the ViewMate® Intracardiac Ultrasound System available from EPMedSystems, Inc. of West Berlin, N.J.

As useful as such intra-organ images can be to a clinician, the imagesobtainable from a catheter mounted ultrasound imaging system arenecessarily limited to two dimensional slice (i.e., cross-sectional)images. This limitation to two-dimensional imaging results fromdimensional limitations inherent in a catheter ultrasound imaginginstrument. On the one hand, an imaging catheter must be less than about10 French (3.3 mm) in size in order to safely access the interior ofhuman organs, such as the heart. A catheter of a larger diameter couldpresent clotting and flow-blockage risks to the patient. Also, largerdiameter catheters are more difficult to bend through the arteries orveins by which access to an organ is obtained. On the other hand,piezoelectric transducers are limited to a minimum size range by theultrasound frequencies desired for imaging purposes. In the intracardiacimaging application, desired ultrasound frequencies range from 3 to 10MHz, and typically range between 5 and 7 MHz. In order to be able toproduce ultrasound within this frequency range, each transducer elementmust have a minimum dimension (length, width and height) ofapproximately 0.2 square millimeters. As a result of these twodimensional limitations (i.e., catheter diameter and minimum transducerdimension), the only configuration possible for a phased array ofpiezoelectric transducers in an intracardiac catheter is a linear arrayaligned with the long axis of the catheter. A conventional intracardiaclinear phased array ultrasound imaging catheter is shown in FIG. 1.

A linear phased array can only generate a two dimensional slice image bysteering the ultrasound beam up and down along (i.e., parallel to) thelong axis of the array. Consequently, a linear phased array ultrasoundimaging catheter acquires a two-dimensional image with an image planeparallel to the long axis of the catheter. Thus, it is not possible todeploy an ultrasound imaging phased array transducer within a catheterthat is capable of generating a three-dimensional ultrasound image.

While the images from an ultrasound imaging catheter can be very usefulfor a variety of diagnostic purpose, the two-dimensional slice imagethey provide shows only a small cross-section of the heart at a time. Ifthe transducer array is oriented to view a cross section of the heartthat contains healthy tissue, the clinician may not detect adjacenttissue which is behaving abnormally or is diseased. In order to viewmost or all of a complex three-dimensional organ such as the heart, theclinician must manually rotate the catheter in order to change therotational orientation of the ultrasound transducer so as to scan theimage plane over the organ. Further, as the heart beats, the surfaces ofthe ventricles and atria move in a complex motion fashion. Thus, it isdifficult for a clinician to visualize the entire heart or comprehendhow the various structures are moving through out the cardiac cycle whenthe clinician is only able to view a single thin slice image at a time.In addition, for some diagnostic applications it will be advantageous togenerate three-dimensional images in order to view significant portionsof an organ at the same time.

To overcome the limitations of a two-dimensional imaging capability,clinicians will typically rotate the catheter my hand during anexamination in order to view different parts of the heart. By rotatingthe catheter back and forth, a clinician can scan the inside of theheart, similar to swinging a flashlight back and forth to view a darkroom.

While this procedure allows the clinician to image much of the heart,this manual solution is necessarily limiting in utility for at leastfour reasons.

First, manual rotation of the catheter adds complexity to a delicateprocedure that involves placement of one or more catheters directly intothe patient's heart. Typically, the clinician will be controlling theangular deflection of the catheter by moving a controller on the base ofthe catheter, positioning the catheter within the heart by inserting orwithdrawing the catheter, adjusting ultrasound imaging parameters,viewing the resulting ultrasound images, and monitoring the patient'scondition, while at the same time trying to mentally assemble the imageslices to “see” the whole heart and search for diagnosticallysignificant details in the images. Manually rotating the catheterrequires the clinician to master a third axis of dexterity.

Second, the clinician must rely upon memory to piece together thevarious views obtained in each of the two-dimensional slices in order tovisualize the three-dimensional structure of the heart. This proceduremay be facilitated in offline analysis when multiple adjacent images maybe displayed on a computer screen simultaneously. However, such methodshave limitations since it is difficult to visualize a three-dimensionalimage of an organ as complex as the heart, and because the viewingperspective (i.e., position and orientation) of the imaging transducermay change from image to image.

Third, the heart is a dynamic organ, moving and changing shape severaltimes per second. Consequently, as the ultrasound imaging transducer isrotated to a new viewing angle, it is imaging the heart at differentinstants in the cardiac cycle. The clinician may attempt to overcomethis disadvantage by slowly rotating the catheter so that imagescovering multiple beat cycles are obtained at each orientation. Howeverthis further complicates the clinician's task by requiring visualizationof the three-dimensional structure which is changing shape constantly.

Fourth, when the clinician manually rotates the catheter, the positionand angular orientation of the transducer array may move in anunpredictable manner. This is due to the fact that the catheter is bentthrough one or more angles in order to position it at the appropriatelocation in the heart for diagnostic imaging. In particular, the tip ofthe catheter containing the transducer array may be held at an angle bysteering wires in the catheter controlled by an actuator in the catheterhandle. Consequently, rotating the catheter may cause the transducer toshift laterally in position and/or rotate upward or downward withrespect to the previous viewing orientation. Also, pressure frommovement of the heart or blood flow may cause the transducer array tomove from image to image. Consequently, a clinician is unable to knowwhether changes in location of imaged structures viewed in subsequenttwo-dimensional slicing images are the result of the shape of the heartstructure, movement of the transducer array with respect to thestructure, or the desired rotation of the transducer array.

As result of these difficulties, current intracardiac ultrasoundcatheter imaging systems have limited ability to generatethree-dimensional images of the heart. Methods for correlatingultrasound images in time, particularly with respect to the cardiaccycle, have been disclosed in U.S. Patent Publication No. 2005/0080336,which is incorporated herein by reference in its entirety.

Thus, there is a need for an ultrasound imaging catheter capable ofrotating the ultrasound imaging transducer about the catheter long axiswith minimal effort by the clinician. Additionally, there is a need forultrasound imaging catheter that is capable of generating ultrasoundimages from known perspectives reliably to facilitate multidimensionalimage generation with minimal impact on the clinician's efforts. Whilecardiac imaging represents a particularly urgent need for such catheterimaging systems, such systems could also be useful in the examination ofother organs.

The various embodiments provide an ultrasound imaging catheter whichincludes a stepper motor that rotates the imaging transducer array toallow the physician to obtain a pan of images spaced about the catheterlongitudinal axis that can then be used to produce composite images ofthe adjacent tissue. The embodiments include a dynamic ultrasoundimaging catheter with a control mechanism for rotating the phased arrayultrasound transducer within the catheter body when positioned withinthe heart or other organ of a patient. This transducer array rotatingcapability enables the clinician to scan the heart and/or obtainsufficient images through a variety of viewing angles in order togenerate three-dimensional ultrasound images of the heart while reducingthe workload of the clinician.

Referring to FIG. 3, an embodiment of an ultrasound imaging catheter 1including an ultrasound imaging assembly 3 at the distal end of thecatheter body 10 and a control/manipulation handle assembly 2 at theproximal end. The ultrasound imaging assembly 3 includes a linear phasedarray transducer 31 positioned within an ultrasound-transparent windowformed by a fluid filled gap 32 and an acoustically compatible tipportion 33. The linear phased array transducer 31 can be mechanicallycoupled to a bearing assembly 35 which fits tightly to the catheter body10, and electrically connected to a wire harness 13 which conductselectrical signals to and from the ultrasound system 150. A rotationaldrive motor 25 at the proximal end of the catheter, such as in thehandle assembly 2, provides a rotational force (e.g., a torque ortension on a wire) to rotate the linear phased array transducer 31 aboutits long axis. In the embodiment illustrated in FIG. 3, a drive wire 36mechanically couples the linear phased array transducer 31 to the drivemotor 25 in the handle assembly 2. The rotational drive motor 25 iselectrically connected by wires 26 to control circuitry (shown in FIG.13) which may be controlled by the clinician through buttons 23, 24 onthe handle assembly 2. Two (or more) steering wires 11, 12 connect toattachment points 14, 15 near the distal end of the catheter body 10(e.g., on the proximal side of the bearing assembly 35) and to adeflection manipulator 22 on the handle assembly 2. In the embodimentillustrated in FIG. 3, the deflection manipulator 22 includes a wheel 28coupled to a spool 29 to which the steering wires 11, 12 are connected.The wiring harness 13 passes through the handle assembly 2 andelectrically connects to conductors in a cable 21 which connects thecatheter assembly 1 to an isolation box 130 coupled to the ultrasoundsystem 150. The cable 21 also includes leads for powering the drivemotor 25 and communicating data regarding the transducer rotationalorientation to the ultrasound system 150.

In the embodiment illustrated in FIG. 3, torque applied by the drivemotor 25 is transmitted to the transducer array 31 by a drive wire 36.The drive wire 36 is made of a material with a diameter sufficient to beflexible yet resist kinking or twisting under torsion. Specifically, thedrive wire 36 needs to be sufficiently flexible so the catheter can bendenough so it can pass through the patient's body and into the heart. Atthe same time, the drive wire 36 needs to be sufficiently resistant tobending to be able to transmit sufficient torque to rotate thetransducer array 31 without twisting into a knot or kink. As usedherein, the term “critical torque” refers to the torque applied to thedrive wire 36 beyond which the wire may twist, kink or deform into aknot. Thus, the drive wire 36 should be of a design (i.e., materialand/or configuration) that has a critical torque that is greater thanthe minimum torque required to rotate the transducer array 31. To meetthese requirements, the drive wire 36 may be a small diameter tube, maybe made of a high strength, flexible metal such as titanium, and/or madeof a material having directional strengthening elements (e.g., carbonnanotubes) within the wire material to provide preferential deflectioncharacteristics.

In embodiments employing a drive wire 36, the transducer array 31 isrotated about its long axis by applying a torque to the drive wire 36using the drive motor 25 positioned at the proximal end of the catheter,such as in the handle assembly 2. To enable the transducer array 31 torotate in response to the applied torque, the transducer array 31 may bemounted on a proximal bearing 35 which allows the transducer array 31 torotate with respect to the catheter body 10. Sufficient slack isprovided in the wire harness 13 so that the wires can twist within thecatheter body 10 as the transducer array 31 turns without binding therotation or pulling an individual wire out of the transducer array.Since the transducer array 31 is rotated approximately 30 to 90 degreesone direction and then 30 to 90 degrees in the other direction, theslack in the wire harness 13 only needs to be sufficient to permit aquarter rotation or less.

Details of an embodiment of the ultrasound imaging assembly 3, includingthe transducer array 31 and bearing 35, are shown in FIGS. 4A and 4B.Referring to FIG. 4A, the transducer array 31 can be coupled to theinner portion of the bearing 35 so that it does not touch the insidesurface of the window portion 33. So supported, the transducer array 31can freely rotate within the fluid filled gap 32 without rubbing thetransducer elements 326 or support structure 322 against the windowportion 33 of the catheter 1. Permitting the transducer array 31 torotate within a fluid filled gap 32 prevents the array from damaging thewindow portion 33 (such as scoring the inside) and the window portion 33from damaging the transducer elements 326 during rotation. Also, theacoustic path between transducer elements 326 and the patient willremain the same as the transducer array 31 rotates.

Fluid within the fluid filled gab 32 provides consistent acousticcoupling between the transducer elements 326 and the acoustic windowportion 33 of the catheter 1. Conventional ultrasound imaging cathetersare designed to avoid gaps between the transducer elements and catheterbody, since such gaps will inhibit sound transmission. Also,conventional ultrasound imaging catheters do not include fluid withinthe catheter, since fluids may cause shorting of electronics. Thus, theinclusion of an acoustic coupling fluid within the catheter in theultrasound imaging assembly 3 region represents a marked departure frompast practice. This acoustic coupling fluid may be selected to have aspeed of sound that is compatible (i.e., nearly the same as) that of theacoustic window portion 33 of the catheter, which maximizes the couplingof ultrasound energy between the transducer elements 326 and theexterior of the acoustic window portion 33. Suitable acoustic couplingfluids include, for example, mineral oil, degassed water, and degassedsaline solution.

Three alternative embodiments are described herein for providing theacoustic coupling fluid to the window portion 33 of the catheter,although other methods may be used and are encompassed within the scopeof the present invention. In a first embodiment, the acoustic couplingfluid is added to the window portion 33 when the catheter is assembled.In a second embodiment, the acoustic coupling fluid is added to thewindow portion 33 just prior to usage, such as by a clinician. In athird embodiment, the acoustic coupling fluid is sterile saline solutionwhich is injected into the proximal end of the catheter assembly to flowthrough the catheter and out the distal end of the window portion 33during use.

In the first embodiment wherein the acoustic coupling fluid is addedduring manufacture, various sealing and fluid expansion features arenecessary as discussed herein with respect to various embodiments. Also,consideration must be made for evaporation and/or degradation of theacoustic coupling fluid during shipping and storage prior to use. Forexample, water or saline solution may evaporate over time, so mineraloil may be preferred for this embodiment. However, mineral oil presentsadded safety concerns which may require additional design features, suchas employing double walls in the portion of the catheter containing thefluid.

In the second embodiment in which the acoustic coupling fluid is addedby a clinician just prior to use, the distal cap 211 can be configuredso that the clinician can securely attach the cap 211 after filing thewindow portion. The sealing mechanism may be any known mechanism,including a threaded connection, a snap fit, a bayonet fit, and/or anadhesive. In this embodiment, the clinician can inject the couplingfluid, such as sterile saline solution by holding the window portionvertically, with distal end up, pouring or injecting (e.g., with asyringe) the fluid into window portion 33, and then sealing the catheterby attaching the distal cap 211. A funnel or other filling aid may beprovided to assist the clinician. Care must be taken not to inject thesaline solution under pressure since dissolved gas may then form bubbleswithin the window portion 33 during operation, which would degradeimaging performance.

In the third embodiment where a stream of sterile saline solution flowsthrough the catheter during use, the catheter assembly includes a porton the handle portion 2 for connecting to a saline source and an openingor vent on the distal tip of the window portion 33 through which salinesolution exits the catheter. Any of a number of known ports for couplinga saline source to a catheter may be used in this embodiment. Ashipping/storage cap (such as the distal cap 211 shown in FIGS. 12A,12B) may be attached to the distal tip of the catheter during assemblyto protect the vent from contamination, with the cap configured to beremoved by the clinician just prior to use. In this embodiment, theclinician may prepare the catheter assembly by coupling the port to asaline source, removing the shipping/storage cap, establishing salineflow until a steady stream free of bubbles exits from the distal vent,and then inserting the catheter into the patient. During operation thesaline solution flows into the patient. Otherwise, the operation of thisembodiment is similar to the various other embodiments. Since theultrasound imaging catheter is a single use instrument, the cathetercomponents need only resist the effects of saline (e.g., corrosion) forthe duration of the examination session.

In an embodiment, a partial acoustic window 332 may be provided over theportion of the catheter through which ultrasound will be transmitted. Inthis embodiment, a particularly thin window or a window of a differentmaterial may be provided to facilitate ultrasound transmission. Forexample, in an embodiment where the transducer array 31 is rotatedthrough 60 degrees, the partial acoustic window 332 would be providedover the 60-70 degrees portion of the circumference of the catheterthrough which ultrasound may be transmitted. This embodiment enables therest of the acoustic window portion 33 to be made thicker or from a morerigid material so that the end portion of the catheter can havesufficient structural rigidity for its intended use and a partialacoustic window 332 with desired acoustic properties.

In order to achieve desired acoustic coupling with blood and tissue, thematerial used to make the partial acoustic window 332 may be selected tohave a speed of sound that is nearly the same as that of blood. Asuitable material for this purpose is Mylar® polyester film.Alternatively, the acoustic window can be made from other materials,such as Pebax® polyether block amide used for the rest of the catheter,provided the window thickness is one-fourth the ultrasound wavelength orless.

FIG. 4C shows a cross sectional view of the window portion 33 for anembodiment employing a Mylar® window 332 a. To manufacture thisembodiment, an opening is cut into the window portion 33 spanning thedesired viewing angle and extending longitudinally along the length ofthe transducer array 32. A Mylar® sheet window 332 a is then plasticweld, bonded or glued onto the window portion 33 (such as on the insidesurface as illustrated) so as to close the opening and form the window332 a. The acoustic coupling fluid within the window portion 33 willmaintain the shape of the Mylar® window 332 a in use.

FIG. 4D shows a cross sectional view of the window portion 33 for anembodiment employing a quarter-wave Pebax® window 332 a. To manufacturethis embodiment, a reduced thickness portion is machined (e.g., by lasermachining) or etched into the window portion 33 spanning the desiredviewing angle and extending longitudinally along the length of thetransducer array 32. Alternatively, the window portion 33 may be formed(e.g., by injection molding or extrusion) with the reduced thicknessportion as illustrated in FIG. 4D.

In an alternative embodiment, the acoustic window portion 33 of the endof the catheter is the same all around. This may be accomplished bylimiting the thickness of the window portion 33 walls to one-quarterwavelength, which would enable the window portion 33 to be made from avariety of materials, including Pebax®, or by manufacturing the windowportion 33 from a material having a speed of sound close to that ofblood, such as Mylar®. This embodiment simplifies assembly of thecatheter assembly since the transducer array 31 need not be rotationallyaligned when inserted into the catheter body 1.

To enable fabrication of the catheter assembly, the distal end of thecatheter body 10 may be sealed with a distal cap 211. In this manner,the catheter body 10 may be slipped over the transducer array 31, wireharness 13, drive wire 36 and other internal elements during assembly,and then sealed by gluing or bonding the distal cap 211. In anembodiment, the fluid filled gap 32 is filled with the acoustic couplingfluid just prior to sealing the catheter body with the distal cap 211.

In order to suspend the transducer array 31 within the fluid filled gap32, the bearing 35 may be of sufficient height (i.e., length along thecenterline) and landed on a bearing seat 350 portion of the catheterbody 10 to resist deflection of the transducer array 31. As shown inFIG. 4A, a bearing seat 350 can be provided in the catheter body 10 witha diameter and length that matches closely that of the bearing 35. A lip350A may be provide on the proximal end of the bearing seat 350 toassist in seating and aligning the bearing 35 and preventing the bearing35 from slipping beyond (i.e., in the proximal direction) the bearingseat 350 during assembly or operation. When the bearing 35 and bearingseat 350 are tightly coupled, such as by way of a compression fit (i.e.,the inner diameter of the bearing seat 350 is slightly smaller than theouter diameter of the bearing 35) or adhesive, the assembly forms acantilever joint sufficient to resist bending loads from the transducerarray 31 and thereby keep the array approximately centered within thefluid filled gap 32.

FIG. 4B illustrates an alternative embodiment in which a second, distalbearing 37 is provided to support the distal tip of the transducer array31 within the acoustic window portion 33 of the catheter. (To avoidconfusion, subsequent references to the bearing 35 positioned on theproximal end of the transducer array 31 will identify it as the“proximal bearing 35” even though some embodiments will only include onebearing.) Suspended between the distal bearing 37 and the proximalbearing 35, both of which contact an inner surface of the catheter, thetransducer array 31 can be centered in the fluid filled gap 32 andprevent from contacting the acoustic window portion 33 of the catheter.The distal bearing 37 can seat on a portion of the distal cap 211 (asshown) or on a seat provided on the acoustic window portion 33 (notshown). This embodiment reduces the dimensional requirements on thebearing seat 350 since the joint formed between the proximal bearing 35and the bearing seat does not need to resist cantilever bending loads.

FIG. 4E illustrates an alternative configuration for a distal bearing37. In this configuration, the distal bearing 37 includes a ring 37 athat contacts the inner surface of the window portion 33, with three (ormore) posts or pads 37 b extending radially inward toward the centerlinea distance sufficient to come in contact with the distal tip of thetransducer array 31. The pads 37 b ensure that the tip of the transducerarray 31 remains approximately centered in the window portion 33 whileallowing the transducer array 31 to rotate. The pads 37 b may be madefrom a low friction material such as Teflon®. Gaps between the pads 37 bthen permit fluid to pass through the distal bearing 37. This featurewill ensure lubrication of the pads 37 b and help enable the functioningof a fluid expansion membrane 212 as illustrated in FIG. 9.

In addition to supporting the proximal end of the transducer array 31,the proximal bearing 35 may be used as a fluid seal to prevent theacoustic coupling fluid within the fluid filled gap 32 from leaking intothe catheter body 10 in some embodiments. This may be accomplished usinga slip bearing such as illustrated in FIGS. 5A and 5B. In theillustrated embodiment, the proximal bearing 35 includes an outerbearing ring 351 and an inner bearing plug 352 separated by a lowfriction bearing surface 353. The bearing surface may be made from a lowfriction material such as Teflon®, which may be a separate piece (e.g.,a thin Teflon cylinder) or a surface coating applied to one or both ofthe outer bearing ring 351 and inner bearing plug 352. When assembled,the low friction bearing surface 353 permits the inner bearing plug 352to turn freely with respect to the outer bearing ring 351, yet forms arelatively fluid-tight seal through the bearing. Additionally, thissimple bearing configuration is easier to assemble than bearingsinvolving rollers or balls, particularly in the diameter suitable foruse in a 10 French or smaller catheter.

In the embodiment illustrated in FIGS. 5A and 5B, the inner bearing plug352 forms an intermediary structure between the transducer array 31 onthe distal side and the wire harness 13 and drive wire 36 on theproximal side. Thus, in this embodiment, the drive wire 36 is connectedto the inner bearing plug 352 so that torque is transferred from thedrive wire 36 to the plug body on the proximal side of the bearing 35(shown in FIG. 5A), and from the plug body to the transducer array 31 onthe distal side of the bearing (shown in FIG. 5B). This connection maybe any mechanical or structural connection sufficient to withstand thecritical torque. For example, the drive wire 36 may be mechanicallyconnected to the plug body by a threaded connection (such as a threadedsleeve over the wire), a latching mechanism, tying or wrapping the wireover a connection piece (e.g., an eyelet), or other known mechanicalconnection, or welded, braised or glued to the plug body, or acombination of both means.

The plug body may also serve as an electrical pathway for the individualcoaxial wires in the wire harness 13 to the transducer array. In asimple configuration, the wires of the wire harness 13 pass through theplug body and connect to the transducer array. This structure avoidsfluid paths along wires in the plug body between the fluid filed gap 32and the rest of the catheter.

By way of example, the inner bearing plug 352 may be formed by over theproximal end of the transducer array 31 and a portion of the wireharness 13 after the electrical connections have been established andconfirmed. The plug body may be formed of molded plastic poured over theend of the transducer array 31 and the connected wires, and thenpolished to the required dimensions. A ring of harder material (e.g., athin metal cylinder) may be slipped over the plastic plug body to form abearing surface. By forming the inner bearing plug 352 in this manner,the plug body can help ensure the integrity of electrical connections tothe transducer array 31 are maintained while the array is rotated.

Another embodiment of the ultrasound imaging assembly 3 is illustratedin FIGS. 6A and 6B. In this alternative, a second fluid seal in the formof a divider disc 240 is provided on the proximal side of the proximalbearing 35. This alternative embodiment is applicable to both the singlebearing embodiment shown in FIG. 6A and the dual bearing embodimentshown in FIG. 6B. Details of the divider disc 240 are illustrated inFIGS. 7 and 8. Therefore, reference is made to FIGS. 6A, 6B, 7A-C and 8in the following description of this alternative embodiment.

Positioning a divider disc 240 proximally removed from the proximalbearing 35 can serve a number of design purposes. For one, the dividerdisc 240 can serve as the structure to which the steering wire anchors14, 15 attach (as shown in FIG. 7A, or as the anchor points (such asholes near the edge of the disc through which or to which the steeringwires 11, 12 are attached). By affixing the divider plate 240 to thecatheter body 10, such as by seating it against a lip or ridge 241 onthe interior of the catheter body 10, bending forces applied by thesteering wires 11, 12 can be conveyed to catheter. By positioning thedivider disc 240 a small distance from the proximal bearing 35, thebearing and bearing seat 350 can be isolated from distortions in thecatheter body 10 due to bending. Thus, catheter bending can be limitedto portion 202 of the catheter while the region 201 between the dividerdisc 240 and the proximal bearing 25 remains relatively straight andundistorted. The divider disc 240 can be made from a number of stiffmaterials, such as Pebax®.

The divider disc 240 can also serve as a second or primary fluid seal toretain acoustic coupling fluid on the distal side of the disc. This canbe accomplished, for example, by passing the wires of the wire harness13 through the disc in fluid-proof seals 243 and providing a fluid tightshaft seal 242 around the drive wire 36. Passing the wires throughdivider disc 240 results in two portions of the wire harness 13, adistal wire harness 13A and a proximal wire harness 13B. To allow forrotation of the transducer array 31, the distal wire harness 1 3A shouldhave sufficient extra length to twist through the angle of rotation ofthe transducer. On the other hand, the proximal wire harness 13B willnot experience twisting.

Referring to FIG. 8, a low friction bearing and fluid-tight shaft seal242 may be formed, for example, by sealing to the drive wire 36 aproximal inner seal plug 245 that fits in the proximal side of a throughhole 247 in the divider disc 240 and distal inner seal plug 246 thatfits in the distal side of the through hole 245 in the divider disc 240.A low friction layer 248 may be provided between the two seal plugs 245,246 and the divider disc 240 to minimize rotational friction.

In an embodiment, the catheter may be provided with a number ofcentering discs 240 i (such centering discs 240 a through 240 f asillustrated in FIG. 7C) that are similar to the divider disc 240.Referring to FIG. 7B, centering discs 240 i may be fashioned as a discwith a diameter approximately equal to the inner diameter of thecatheter body 10, having a central low friction bearing 242 such as thatdescribed above with reference to FIG. 8. Since the centering discs 240i may not be fluid boundaries, they may include through holes 249 (e.g.,three or four holes as illustrated in FIG. 7B) through which the wireharness 13 and steering lines 11, 12 can be threaded. In embodiments inwhich the entire catheter 1 is filled with the acoustic coupling fluid,such as the embodiments in which sterile saline solution is continuouslyinjected into the proximal end of the catheter during use, thethrough-holes 249 provide paths for the acoustic coupling fluid to pass.

A primary function of centering discs 240 i is to ensure the drive shaft36 remains approximately centered in the catheter body 10 as thecatheter is bent. Since the drive shaft 36 may have different bendingcharacteristics, it may follow a different radius of curvature than thatof the catheter body 10 through a bend. This could cause some of therotational torque to be translated into displacement forces applied tothe catheter body 10, which could result in the catheter moving duringscanning operation as well as introducing errors into the transducerrotational orientation. To avoid the potential for such problems, two ormore centering discs 240 i may be provided at intervals along theportion of the catheter body 10 that will experience bending. Asillustrated in FIG. 7C which shows six centering discs 240 a through 240f in addition to the divider disc 240, the centering discs 240 i help tomaintain the drive shaft 36 along the centerline of the catheter body10.

As illustrated in FIG. 7B, the through-holes 249 in the centering discs240 i can be used to separate the wire harness 13 and the steering wires11, 12 from the drive shaft 36 to prevent tangling during oscillationoperations when the drive shaft 36 will be rotating rapidly. Asillustrated in FIG. 7C, the centering discs 240 i can be also be used tothread the steering wires 11, 12 so they lie on the same side of thecatheter body 10, which reduces the steering errors since the pathlength of the steering wires 11, 12 through the catheter remains thesame as the catheter bends. For example, the steering wires 11, 12 maypass through through-holes 249 on opposite sides of centering discs 240a and 240 b, and then be brought together so they pass through the samethrough-hole 249 in subsequent centering discs 240 c-240 f. Thisconfiguration can be used to apply proper bending torque to the dividerplate 240 while passing the steering wires 11, 12 along the same side ofmost of the catheter body 10.

Operation of the embodiment illustrated in FIGS. 6A, 6B, 7A-C and 8 issimilar to that of the embodiments illustrated in FIGS. 4A and 4B.Further, the centering discs 240 i described above with reference toFIGS. 7B, 7C may be implemented with the embodiments illustrated inFIGS. 4A and 4B.

In the various embodiments which include a sealed catheter assemblywherein the acoustic coupling fluid is provided during manufacture,provisions must be made to accommodate expansion/contraction of theacoustic coupling fluid with temperature changes. Operation of thetransducer elements 326 will heat the acoustic coupling fluid, whichwill cause the fluid to expand. During shipping and storage, thecatheter may be subjected to cold temperatures (e.g., while be shippedduring the winter) which will cause the acoustic coupling fluid tocontract, as well as hot temperatures (e.g., while being shipped duringthe summer months) which will cause the acoustic coupling fluid toexpand. To avoid damage to the transducer array 31, bearings 35, 37 andacoustic window portion 33 of the catheter, a fluid reservoir can beincluded to accept excess fluid when the fluid expands and ensure thefluid filed gap 32 remains filled when the fluid contracts. To a certainextent, fluid volume changes can be accommodated by flexure of theacoustic window portion 33 of the catheter.

An example of a fluid expansion reservoir is illustrated in FIG. 9. Inthis example embodiment, the catheter distal cap 211 includes a flexibleexpansion membrane 212 which can flex into and out of an expansionvolume 213 within the distal cap 211. Vent holes 214 in the distal cap211 allow air or fluids to pass through the cap to accommodatedisplacement of the expansion membrane 212. In this example, theexpansion membrane 212 extends into the fluid filled gap 32 when theacoustic coupling fluid is cold (i.e., at minimum volume), and expandsoutward into the expansion volume 213 (such as to extended position212A) as the acoustic coupling fluid heats up. By controlling the sizeand shape of the expansion membrane 212 and size of the expansion volume213, the maximum and minimum volumes of the acoustic coupling fluid canbe accommodated. Other fluid reservoir and expansion mechanisms known inthe mechanical arts may also be used. It is worth noting that thepresence of the acoustic coupling fluid in the catheter will require useof non-thermal methods of sterilization, such as chemical cleaningand/or gamma irradiation.

While the foregoing embodiments include fluid seals in the proximalbearing 35 and/or divider disc 240 to retain the acoustic coupling fluidin the distal portion of the catheter, in other embodiments the entirecatheter can be filled with fluid. These embodiments simplifyfabrication by eliminating the need for providing fluid-tight seals inthe vicinity of the transducer array 31. In one of these embodiments,one or more fluid boundary seals, like the divider disc 240 illustratedin FIGS. 6A, 6B, 7A and 8, are positioned near the proximal end of thecatheter body 10 to prevent the acoustic coupling fluid from reachingthe handle. In another embodiment, the acoustic coupling fluid fills theentire catheter and a portion of the handle assembly 2 including thedrive motor 25 and the deflection spool 29. These alternativeembodiments may not require volume compensation mechanisms, since theexpansion of the acoustic coupling fluid with temperature can beaccommodated by elastic expansion of the entire catheter body 10.

While the foregoing embodiments employ a drive wire 36 to transferrotational torque to the transducer array 31, other mechanisms forrotating the transducer array 31 may be used. For example, FIGS. 10A-10Eand 11A-11E show alternative embodiments in which the rotational forceis provided from a drive motor 25 in the handle assembly 2 to thetransducer array 31 by tension lines 361, 362 which wrap around one ortwo drive spools 368, 369 coupled to a short drive wire 336 thattransmits torque to the array.

Referring to FIG. 11A, rotational energy from the drive motor 25 turns adrive motor spool 365 which transfers the rotational energy into tensionin tension lines 361, 362 wrapped about the drive motor spool 365. Whenthe drive motor spool 365 turns in one direction, tension line 361 ispulled toward the handle, for example, while tension line 362 is playout away from the handle an equal amount. Similarly, turning the drivemotor spool 365 in the opposite direction applies tension to tensionline 362 while playing out tension line 361. Line guiding structures,such as pulleys 366, 367 mounted on the handle assembly 1 by structures370, may be use to direct the drive wires into the catheter body 10,although the drive motor spool 365 may be oriented so no pulleys arenecessary.

Near the distal end of the catheter 1, the tension lines 361, 362 passthrough turning blocks 363, 364 which direct the tension lines 361, 362onto one drive spool 368, in the embodiments shown in FIGS. 10B-10D, ortwo drive spools 368, 369, in the embodiment shown in FIG. 10A. Thetension lines 361, 362 are wound onto the drive spool 368 (or drivespools 368, 369) so that when tension is applied to one of the tensionlines 361 or 362, the drive spool 368 (or 369) turns to play out line.As the tension line 361 or 362 turns the drive spool 368 (or 369),torque is applied to a short drive shaft 366 coupled to the drive spool368, (or drive spools 368, 369) which transmits the torque to thetransducer array 31 through a bearing 35 in the manner described above.The proximal end of the short drive shaft 366 may be supported in thecatheter body 10 by a proximal drive shaft bearing 365 in order toresist bending forces due to tension on one tension line or the other.Grooves or through holes in the proximal drive shaft bearing 365 may beprovided to allow the drive wires 361, 362 to pass through the bearingto reach the turning blocs 363, 364.

In the embodiment illustrated in FIG. 10A, each tension line 361, 362 iswound onto its own drive spool 363 or 364. The tension lines are woundin different directions, so when one tension line (e.g., 361) is pulledcausing it to unwind from its drive spool (e.g., 369), the other tensionline (e.g., 362) is wound onto its drive spool (e.g., 368). The wireharness 13 passes through drive spools 368, 369 to connect with thetransducer array 31 as described above with reference to FIG. 3. Sincethe two drive spools are positioned adjacent to each other along thelongitudinal axis, the turn buckles 363, 364 will be at different axialpositions along the catheter body 10, which may allow them to bepositioned on the same side of the catheter. The tension lines 361, 362are firmly attached to their respective drive spools 368, 369 so thatwhen fully unwound the lines do not come free from the spool.

In the embodiment shown in FIG. 10B, only a single drive spool 368 isemployed, with the tension lines 361 and 362 winding onto the spool inopposite directions. In this embodiment, the tension lines 361, 362 maybe a continuous line that wraps a number of times around the drive spool368, or two separate lines each firmly attached to the spool. Since thetension lines 361 and 362 wind onto the drive spool 368 in oppositedirections (and therefore on opposite sides), when the spool turns tolet out one line (e.g., 361) it simultaneously winds in the other line(e.g., 362) an equal amount. Resulting torque applied to the drive spool368 is conveyed to the transducer array 31 by the short drive shaft 366which may be supported by a proximal drive shaft bearing 365. As withthe previously describe embodiment, the wire harness 13 passes throughdrive spool 368 to connect with the transducer array 31 as describedabove with reference to FIG. 3.

While the embodiments illustrated in FIGS. 10A and 10B employ a shortdrive shaft 366, the rotational torque may be conveyed from the drivespool 368 to the transducer array 31 by a drive cylinder 367 asillustrated in FIG. 10C. In this embodiment, the drive cylinder 367 mayencompass the wire harness and the drive spool 368 may be a ring withraised edges (to retain the drive wires 362, 362) positioned over andcoupled to the cylinder. The routing and winding of the tension lines361, 362 may be similar to that of the embodiment shown in FIG. 10B.Since the drive cylinder is hollow, the wire harness 13 can pass throughthe cylinder and the proximal drive shaft bearing 365 to connect withthe transducer array 31 as described above with reference to FIG. 3.

The proximal drive shaft bearing 365 shown in FIGS. 10A-10C helps tostabilize the drive shaft 366 or drive cylinder 377 within the catheterbody 10 and resist bending forces applied by the tension lines 361, 362.However, the proximal drive shaft bearing 365 may be dispensed with inembodiments where the proximal bearing 35 and short drive shaft 366 ordrive cylinder 367 are rigid enough to resist the cantilever bendingforces applied by the tension lines 361, 362. For example, in anembodiment shown in FIG. 10D, the drive spool 368 can be directlycoupled to the inner bearing plug 352 of the proximal bearing 35 so thebending forces applied by the tension lines 361, 362 are resisted by thebearing 35 directly, thereby minimizing cantilever bending stresses. Inthe embodiment shown in FIG. 10D, the drive spool 368 may be glued,brazed or welded to the inner bearing plug 352, or may be an extensionof the inner bearing plug 352 itself. In this embodiment, the wireharness 13 passes through the drive spool 368 and inner bearing plug 352to reach the transducer array 31. While FIG. 10D shows a single drivespool 368, two drive spools may be employed, with a second drive spool(369) coupled to the proximal side of the first drive spool 368 and thewires routed and wound as described above with reference to FIG. 10A.

An alternative embodiment for the drive spool 368 is illustrated in FIG.10E that obviates the need for turn buckles 363, 364. In thisembodiment, the drive spool 368 includes two winding grooves 368 a, 368b disposed approximately on opposite portions of the spool. A dividerplate 369 is provided on a proximal side and slightly removed from thedrive spool 368, with through-holes 369 a, 369 b near the peripherythrough which the drive wires 361, 362 pass. The diameter of the drivespool 368, the inclination of the winding grooves 368 a, 368 b, thedistance between the drive spool 368 and the divider plate 369, and theradial separation between through-holes 369 a, 369 b are configured sothat the drive wires 361, 362 experience a small angle as they exit thethrough-holes and wind directly onto the winding grooves 368 a, 368 b.So configured, the drive wires 361, 362 will play directly onto thedrive spool 368 with low friction, thereby eliminating for a turn buckleor other mechanism to guide the wires onto the drive spool 368. Byproviding winding grooves 368 a, 368 b on opposite sides of the drivespool 368, oscillating motion can be induced by alternatively pulling onone drive wire 361 followed by pulling on the other drive wire 362.

A drive spool with inclined winding grooves may also be employed on thedrive motor side (i.e., proximal end of the catheter) to eliminate theneed for turn buckles. Referring to FIG. 11B, the drive spool 365 acoupled to the drive motor 25 can include inclined winding grooves 365 band 365 c onto which the tension lines 361, 362 are threaded. Byaccepting the tension lines at an angle to the circumference, the turnbuckles can be replaced with a divider plate 371 with through holes fordirecting the tension lines 361, 362 at a slight angle from the catheteron to the drive spool 365 a. As with the drive spool assembly on thedistal end, the diameter of the drive spool 368, the inclination of thewinding grooves 368 a, 368 b, the distance between the proximal drivespool 365 a and the divider plate 371, and the radial separation betweenthrough-holes are configured so that the drive wires 361, 362 experiencea small angle as they exit the through-holes and wind directly onto thewinding grooves 365 b, 365 c. So configured, the drive wires 361, 362will play directly onto the drive spool 365 a with low friction, therebyeliminating for a turn buckle or other mechanism to guide the wires ontothe drive spool 365 a. By matching the diameter of the proximal drivespool 365 a to that of the distal drive spool 368, a rotation of thedrive spool on the handle will result in an equal rotation of the distaldrive spool and thus the transducer array.

In the various embodiments, the distal end of the catheter 1 can bedeflected or steered by manipulating the deflection manipulator 22 onthe handle assemble 2. Mechanisms for deflecting or steering ultrasoundimaging catheters are disclosed in U.S. Patent Application PublicationNo. 2005/0228290, the contents of which are incorporated herein byreference in their entirety. In general, when the deflection manipulator22 is turned (or slide for slide manipulator configurations), tension isapplied to one steering line 11 while tension is eased on the othersteering line 12. Tension on steering line 11 pulls on the attachmentpoint 14 coupled to the catheter body 10 near the distal end. Thistension causes the distal portion to bend toward the side in tension.Steering the other direction is accomplished by reversing the motion onthe deflection manipulator 22, which places steering line 12 in tensionand eases steering line 11. The attachment points 14, 15 for thesteering lines 11, 12 may be provided in a number of configurations,including directly coupled to the catheter body 10, to a portion of thetransducer array structure 3, to a proximal side of the bearing 35, to aring in firm contact with the catheter body 10, or a disc (as shown inFIG. 7) in firm contact with the catheter body.

In an alternative embodiment, the catheter body 10 may include steeringwires within the walls of the catheter, obviating the need to pass thesteering wires through interior. Such catheters are commerciallyavailable, and therefore further description of the steering wireconfigurations is unnecessary.

In embodiments employing tension lines 361, 362 to transmit rotationaltorque to the transducer array 31, the tension lines may also be used todeflect or steer the distal portion of the catheter 1. In thisembodiment, transducer array 31, bearings 35, 37 and/or the drive spool368 include a mechanism that prevents the transducer array 31 fromrotating beyond a certain angle (e.g., ±30 degrees). For example, thismechanism may be a physical stop one or in the bearing 35 or drive spool368 like a tab on a rotating surface that engages a tab on catheter body10 at the maximum rotation angle. As another example, the tension lines361, 362 may be anchored to the drive spool 368 so that at the maximumrotation angle one of the tension lines 361 or 362 is completely unwoundfrom the spool and tension is applied directly to the spool. In thisembodiment, the deflection manipulator is replaced by an operationalmode for the drive motor 25 which may be controlled by the buttons 23,24 on the handle assembly 2. To deflect the distal portion of thecatheter is this embodiment, the transducer array 31 is rotated to itsmaximum rotation angle by the drive motor 25 and then further tension isapplied by the drive motor 25 to the tension line 361 or 362. Withfurther rotation of the drive spool 368 stopped, force from the linetension will be applied to the corresponding turn buckle 363 or 364which will apply a bending force to the catheter body 10, causing thedistal portion to deflect or steer. To deflect the catheter in theopposite direction, the drive motor 25 is run in the opposite directionuntil the transducer array 31 is rotated to its opposite maximumrotation angle and further tension is applied, which applies a bendingforce to the catheter body 10 through the other turn buckle 364 or 363.It should be noted that this embodiment does not allow the deflectioninduced using drive wires 361, 362 to be maintained during ultrasoundscanning. Therefore, this deflection mechanism may be used inconjunction with the steering wire deflection mechanism described hereinwith reference to FIG. 3, such as to provide a second plane ofdeflection useful during the catheterization process. Also, electronicmeasures may be implemented to prevent the drive motor 25 from turningthe transducer array 31 to the rotational stops during ultrasoundimaging in order to prevent inadvertent deflection of the ultrasoundimaging assembly 3.

A variety of drive motors 25 and motor configurations may be used in thevarious embodiments. In one embodiment, the drive motor 25 is a steppermotor that allows for precise control of the rotation of the drive shaftas the motor moves one angular increment (i.e., step) at a time. In thisembodiment, the drive motor 25 can be advanced a single step or a fewsteps and then held in that orientation while one or more ultrasoundframes are obtained, before being advanced to the next step (or fewsteps). The drive motor 25 may alternatively be a continues motionmotor, in which case an orientation sensor, such as an optical discsensor, may be included in the motor assembly so the controller candetermine the orientation of the drive shaft 36 or drive spool 365.

In another embodiment illustrated FIG. 11C, in the drive motor 25 mayinclude a gearing mechanism, such as a small gear 252 coupled to themotor 25 rotor that engages a larger gear 251 coupled to the drive shaft36 or drive spool 365, using any number of well known gearingmechanisms. Providing a gear assembly 251, 252 between the drive motor25 and the drive shaft 36 or drive spool 365 can increase the torqueapplied to the drive shaft 36, adjust the rotational rate of thetransducer array with respect to the motor rotation rate, and/or allowthe drive motor 25 to be a reusable part that connects to the gearassembly 251, 252 when the catheter 1 is coupled to the handle 2 justprior to use.

In a further embodiment, the drive assembly may include a rotationsensor to inform the handle controller or system controller of theposition of the transducer array. For example, FIG. 11C shows a rotationsensor 256 coupled to the drive motor 25, such as by a gear 255, torecord the rotational orientation of the drive shaft 36 or drive spool365. The rotation sensor 256 may be any of a number of commerciallyavailable rotation counters that generates a signal transmitted by aconductor 257 to the handle controller or system controller. FIG. 11Calso shows an alternative rotation sensor including an optical sensor253 configured to sense optical properties on the large drive gear 251to sense the rotational orientation of the gear. Such an optical sensor253 may read markings, optical properties, or other indicia on the drivegear 251 and provide a signal via a conductor 254 to the handlecontroller or system controller which can use information in the signalto determine the gear's rotational orientation, and thereby estimate thetransducer's rotational orientation. A third configuration for arotation sensor is illustrated in FIG. 11D, which includes an opticallyencoded disc 258 coupled to an axel 253 or drive shaft 36 coupled to thelarge drive gear 251, and an optical sensor including an illuminatorpart 253 a and light sensor part 253 b. The illuminator part 253 a andlight sensor part 253 b are positioned on either side of the opticallyencoded disc 258, as illustrated, or on the same side of the opticallyencoded disc 258, so that the light from the illuminator part 253 a istransmitted through or reflected off of the optically encoded disc 258and received by the light sensor part 253 b. The optically encoded disc258 includes optical properties, shapes or patterns that enable acontroller to determine the rotational orientation of the disc basedupon signals received from the light sensor part 253 b. For example, theoptically encoded disc 258 may include a circumferential stripe near theouter rim that exhibits a transparency gradient, such as ranging from100% transparent to 100% opaque, which may be generated using a numberof photographic or computer-image generating processes. With such agradient stripe, a controller receiving a light intensity signal fromthe light sensor part 253 b can calculate the rotational orientationbased upon the amount of light transmitted. Alternatively, theilluminator part 253 a and light sensor part 253 b may be positioned onthe same side of the optically encoded disc 258 and the circumferentialstripe feature a continuous gradient from 100% transparent to 100%reflective. In both of these alternatives, the controller can calculatethe value of received light intensity divided by the intensity of thelight source, a fraction that can be correlated to the rotationalorientation of the optically encoded disc 258.

In another embodiment of the drive motor 25, the motor's rotor portion25 a may be sealed within a thin walled portion 10 a of the catheterbody 10 that is configured to slip into a reusable stator portion 25 bpositioned in the handle. This alternative enables the catheter assembly1 to be fashioned as a fully sealed unit that slips into a reusablehandle 2 which includes a reusable stator portion 25 b of the motor 25.This embodiment may include a rotor 25 a coupled to a rotor shaft 253that is rotatably fixed on both ends, such as via a first bearing in adivider plate 371 and a second bearing 255 in the thin walled portion 10a of the catheter body 10. The stator portion 25 b may be sealed withina portion of the handle structure 220, with an opening 221 configured toaccept the thin walled portion 10 a of the catheter assembly. The rotorportion 25 a may be coupled to either a drive shaft 36 or a drive spool365 according to any of the embodiments described herein.

In a further embodiment, the stator of the drive motor 25 may beremovable and configured to slip over the rotor of the drive motor 25when the catheter 1 is coupled to the handle 2 just prior to use. Thiswould allow reusing a portion of the drive motor 25 while providing thecatheter assembly 1 as sterile, sealed assembly.

Another embodiment of the distal portion of the catheter assembly 1,which is illustrated in FIGS. 12A-12C, includes a flexible fluid seal310 coupled between the catheter body 10 and a portion of the transducerarray 31. Referring to FIGS. 12A and 12B, the flexible seal 310 may bemade of Mylar® or other flexible plastic sheet material with sufficientexcess material to allow the transducer array 31 to rotate with respectto the window portion 33. For example, sufficient excess material in theflexible seal 310 may permit the transducer array to turn approximately45 degrees one direction and 45 degrees in the other direction toprovide a total rotation angle of 90 degrees. Since the dynamicultrasound imaging catheter is a single use device, the flexible seal310 can be designed to last a limited number of cycles. Using a flexiblefluid seal 310 coupled between the catheter body 10 and a portion of thetransducer array 31 allows the bearing device at the proximal end of thetransducer array to be a simple slip ring 250, saving on the cost andcomplexity of a fluid boundary bearing as described above. In thisembodiment, the transducer array 31 may include an extension shaft 311aligned with the centerline of the transducer array 31 and extending adistance in the proximal direction to provide an attachment surface forthe a flexible fluid seal 310 and a bearing surface for rotationallyinterfacing with the slip ring 31. The proximal end of the extensionshaft 311 can connect to a drive wire 36, as illustrated in FIG. 12A, orto a drive spool 368, as illustrated in FIG. 12B. Also, the wire harness13 may connect to or through the extension shaft 311. In thisembodiment, the transducer array 31 is maintained in the center of thewindow portion 33 of the catheter by the slip ring 250 encircling theextension shaft 311 on the proximal end and by a distal bearing 37 likethat illustrated in FIG. 4E encircling or contacting a distal portion ofthe transducer array 31. As described herein with respect to otherembodiments, the end cap 211 illustrated in FIGS. 12A and 12B may beremovable prior to use, or a self sealing cap of any number of knownconfigurations.

Referring to FIG. 12C, the slip ring 250 may be a simple disc with acenterline through-hole 252 sized to be slightly larger than theextension shaft 311. The centerline through-hole 252 may be coated witha low-friction coating, like Teflon®, or the slip ring 250 itself may bemade from a low-friction material like Teflon® so that the extensionshaft 311 can turn freely. Peripheral through-holes 251 may be providedin the slip ring 250 to permit fluid to flow through it or to allowpressures to equalize on both sides of the slip ring 250 so that theextension shaft 311 is not longitudinally displaced by pressuredifferences between the proximal and distal ends of the catheter.

In embodiments in which the acoustic coupling fluid is added to thewindow portion 33 at the time of use, the clinician may remove the endcap 211 and pour or inject the acoustic coupling fluid through thedistal bearing 37. For example, the distal bearing 37 illustrated inFIG. 4E includes gaps between the pads 37 b through which the acousticcoupling fluid can be introduced. A filling tool may be used, such as afunnel or a syringe, in this process, though care should be taken toavoid introducing bubbles into the window portion. Once the windowportion 33 has been filled with acoustic coupling fluid, the end cap 211can be reattached, such as by pressing on it to form a snap seal.

In an embodiment in which sterile saline solution is flowed through thecatheter during operation, the distal portion of the catheter may usethe slip ring 250 and distal bearing configuration as illustrated inFIGS. 12A-12C with the exception of the flexible seal 310. In such anembodiment, the end cap 211 is removed prior to injecting salinesolution at the time of use. The through-holes 251 in the slip ring 250permit saline solution to flow freely into the window portion 33, andgaps in the distal bearing 37 between the bearing pads 37 b illustratedin FIG. 4E permit saline solution to exit the tip of the catheter.

Control of the dynamic motion of the transducer array 31 can beaccomplished using circuitry similar to that illustrated in FIG. 13.Torque is applied to the drive wire 36 by an electric motor 25 which maybe a stepper motor 25 or other electric motor. Power to the motor 25 canbe provided by a power control circuit 902 coupled to an electric powersource 903 and controlled by a controller 901 by means of leads 910,911. The power control circuit 902 provides power from power source 903with polarity and in increments (e.g., pulses or steps) in response tocommands received from the controller 901. The power control circuit 902may be one or more power transistors that are gated on/off by signalsreceived from leads 910, 911. The controller 901 receives control inputsfrom an operator by buttons 23, 24, for example, which may be simpleswitches 923, 924 that provide simple on/off signals on inputs to thecontroller 901. The controller 901 can receive signals from the motor 25via lead 913 and/or the power control circuit 902 via lead 912 that itcan use to determine the position of the transducer array 31, asexplained below. The buttons 23, 24 are optional because the controller901 can receive control inputs from the ultrasound system 150, which mayrun an autonomous scanning routine and/or receive user inputs viakeyboard, mouse, touch-screen or other user interface device. Thecontroller can also provide status and transducer orientationinformation to the ultrasound system 150 and receive timing and motorcontrol signals from the ultrasound system 150 via input/output leads915.

The controller 901 may be a microprocessor or microcontroller withinternal or external memory positioned within the handle assembly 2,within the isolation box 130 or within the ultrasound system 150.Alternatively, the controller 901 may be incorporated within theoperating software of the ultrasound system 150 itself. The power source903 may be a battery (e.g., one or more disposable batteries) withinhandle assembly 2 or isolation box 130, or may be a power source (e.g.,a DC power supply) within the ultrasound system 150 itself.

In an embodiment, each of the components shown in FIG. 13 can bepositioned within the handle assembly 2. In other embodiments, only thebuttons 23, 24, motor 25 and power control circuits 902 are positionedin the handle assembly, with the other components and functionspositioned or performed in the isolation box 130 or ultrasound system150. In yet another embodiment, only the motor 25 is positioned withinthe handle assembly with the other components positioned within acatheter holder assembly (not shown), the isolation box 130 and/or theultrasound system 150.

In embodiments employing a drive wire 36, software or circuitry basedmechanisms may be included to prevent kinking of the drive wire 36. Inan embodiment, the drive motor 25 is configured to produce a maximumtorque that is less than a critical torque that could cause the drivewire 36 to kink. This may be achieved by limiting the power of the drivemotor 25, or by monitoring the power applied to the drive motor 25, suchas with the controller 901, and cutting off power to the drive motor 25before the critical torque level is reached. In a further embodiment,the controller 901 (or the drive motor 25) may be programmed andconfigured to limit drive motor 25 rotation so that it does not turn thetransducer array 31 beyond its rotational limits. Additionally,centering discs 240 i positioned periodically along the catheter body 10will help prevent kinking of the drive wire 36 under torque conditions.

While not specifically shown in FIGS. 3-13, the various embodimentsinclude a temperature sensor, such as a thermistor as illustrated inFIG. 2, positioned near the transducer array 31 so as to sense thetemperature of tissues exposed to ultrasound energy. Signals from thetemperature sensor are routed to the isolation box 130, and in someembodiments, to the ultrasound system 150 so that ultrasound imaging canbe automatically terminated if tissue temperatures approach a dangerouslevel.

The various embodiments provide a maximum scanning angle through whichthe transducer array 31 can be rotated. This maximum scanning angle maybe 30, 60, 90, 120 or 180 degrees, for example, or any angle in between.The limiting design factor in determining the maximum scanning angle isthe maximum twist that can be sustained by the wire harness 13 or othercatheter components (e.g., a flexible seal 310). As the transducer array31 rotates, the distal end of the wire harness 13 rotates with it whilethe proximal end remains fixed. In embodiments where the wire harnesstwist extends over most of the length of the catheter 1, such as inembodiments shown in FIGS. 3, 4A, 4B, and 10A-10D, a larger scanningangle (e.g., 90 to 180 degrees) may be implemented without causing thewire harness to tangle or pull out of connections at either end of thecatheter. In embodiments where the wire harness twist extends over alimited distance, such as in embodiments shown in FIGS. 6A and 6B, themaximum scanning angle may need to be limited, such as to 60 degrees orless, to avoid tangling or placing the wire harness 13 in tension suchthat electrical connections are broken. By providing extra length (i.e.,slack) in the portion of the wire harness 13 that will experiencetwisting, the maximum scanning angle can be increased. When implementinga particular embodiment, the maximum scanning angle may be determinedbased upon physical limitations, such as maximum allowable wire harnesstwist, and then implemented in the control circuitry and/or softwarecontrol instructions so that operational scanning angle is less than themaximum physical scanning angle in order to prevent damage to thetransducer array 31 and wire harness 13.

A dynamic imaging catheter system according to the various embodimentsmay be used in conjunction with an ultrasound system as illustrated inFIG. 14. A user may interface with a top level system controllerfunctionality within the ultrasound system (e.g., by means of a mouseand keyboard) to define basic parameters of the ultrasound imaging to beconducted, step 1401. For example, the user may specify the rate atwhich the volume images are to be refreshed (i.e., re-imaged) and thedesire minimum resolution desired. The user may also define the size ofthe volume to be imaged in terms of scan angle (or frame angle),transducer rotation angle, and imaging depth. As a further input, theuser may select a feature in the ECG signal to use as an imagingtrigger, set an ECG test condition (e.g., a test to detect atrialfibrillation), or select an imaging program based upon the ECG status.

In selecting these various imaging parameters, the ECG status may beconsidered by the clinician to determine the appropriate imaging programto employ. For example, in a normal heart indicated by a normal ECGpattern, the heart exhibits periods of relative rest 1407 in which therewill be less movement frame-to-frame in a dynamic image scan. Thus, in anormal heart, the appropriate imaging program may consist of a series offull ultrasound frames may be taken at each of a number of rotationalorientation steps across the entire rotational range. A healthy heartimaging program may also include obtaining two or more frames perorientation step to obtain more image data and thus enable better imageprocessing. Also, imaging operations may be conducted to exclude the QRScomplex, imaging only during the intra-beat periods 1407.

However, in a diseased heart exhibiting atrial fibrillation, forexample, the heart may exhibit continuous, high-frequency movementsindicated by rapid irregular ECG signals 1408. With the heart quiveringunpredictably, heart tissue is likely to move enough to cause imageblurring (or blurring of compound images) over the span of a fullrotation scan, and even over a full frame scan (i.e., maximum sweepangle). In such conditions, the appropriate imaging program may consistof performing many short duration scans across less than the full sweepangle per frame and less than the entire rotational range. By increasingthe frame rate (i.e., number of two-dimensional images per second),clear images of the rapidly moving heart may be obtained. Since framerate is inversely proportional to viewing angle and inverselyproportional to imaging depth, the imaging program may involve reducingthe viewing angle and/or the imaging depth. Additionally, the rotationrate of the transducer array may be increased to obtain an image volumethat represents very short intervals of time. Alternatively, therotation step size may be increased so that a complete scan can beobtained in fewer steps. Also, the imaging may be conducted for a longertime, covering much of the atrial fibrillation period 1408, in order toobtain more data for viewing and image processing.

Once the user has selected the appropriate ultrasound imagingparameters, the system controller function may provide these parametersin the form of commands to the master controller function. The mastercontroller then determines when images should be acquired, calculatesthe necessary rotation step size, rotation rate and sweep angle toobtain ultrasound image consistent with the user supplied parameters,step 1402. The master controller then provides control signals to thestepper motor controller function. The stepper motor controller convertsthe received control signals into electrical pulses supplied to thestepper motor which determines the direction and number of steps themotor moves through before stopping, step 1403. The stepper motor thenturns in response to the electrical pulse provided by the stepper motorcontroller, step 1404. When the stepper motor stops at a step, thesystem acquires one or more image frames, step 1405. These image framesare transmitted by the ultrasound imaging catheter as ultrasound signaldata to the ultrasound imaging system, which stores the image data andgenerates a display, step 1406.

Depending upon the displayed imagery, the user may adjust imagingparameters, repeating step 1401, in order to obtain better or differentimage resolution. Also, if the user observes a change in the ECGpattern, the user may initiate a different imaging program asappropriate.

The ultrasound system may also receive ECG signals directly and, using apattern recognition algorithm, detect when the heart is in a normalrhythm or in an abnormal state, such as atrial fibrillation, andautomatically select the appropriate imaging program to use.

In the foregoing process illustrated in FIG. 14, the system controllerfunction 1401, the master controller 1402 and the steps of acquiringimages 1405 and displaying images 1406 may all be accomplished insoftware operating on one or more system processors (e.g.,workstations). In an embodiment, each of these functions may be separatesoftware modules operating on the same workstation processor. In thisembodiment, the system processor is adapted and configured by operatingsoftware and electronic connections, including connectors forelectrically connecting to the ultrasound imaging catheter, to directthe rotation of the transducer array using the stepping motorcontroller, to direct the acquisition of ultrasound image data, toreceive the ultrasound data, generate ultrasound image frames from theultrasound data, and display the ultrasound images. In anotherembodiment, the functions may be accomplished in software operating onmultiple processors, such as a system processor running systemcontroller and master controller software modules coupled to anultrasound imaging system workstation operating software to perform theimage acquisition 1405 and image display 1406 functions.

During the imaging process, it is important for the imaging systemprocessor to be able to estimate the rotational orientation of thetransducer array at the instant an image frame is obtained. However, thetransducer array is at the distal end of the catheter, which makes itdifficult to directly measure its orientation. Methods for estimatingthe transducer orientation are disclosed in U.S. patent application Ser.No. 11/610,357 entitled “Catheter Position Tracking for IntracardiacCatheters” and Ser. No. 11/610,386 entitled “Catheter Position TrackingMethods Using Fluoroscopy and Rotation Sensors,” both filed on Dec. 13,2006, both of which are incorporated by reference in their entirety.Additionally, the transducer rotational orientation may be estimated bythe imaging system processor based upon information obtained by theprocessor from the stepper motor and an optional rotational orientationsensor 253, 256, as illustrated in FIG. 15. In this method, the afterthe drive motor has rotated an increment, step 1501, the drive motororientation is communicated to the system processor, step 1502. Thedrive motor orientation may be obtained from the stepper motorcontroller or a separate rotational orientation sensor 253, 256. Therotational position of the stepper motor does not necessarily correspondto the rotational orientation of the transducer array due to twisting ofthe drive wire 36 or stretching of the drive line 361, 362. Tocompensate for this, the torque applied to the drive wire 36 or drivespool 365 may be measured and communicated to the system processor, step1503. Torque may be measured by any number of known mechanisms. Havingdata both the drive motor orientation and applied torque to hold thepresent rotational position, the system processor can then estimate thetransducer's rotational orientation, step 1504. Assuming constantelasticity of the drive wire 36 or drive line 361, 362 over the range ofapplied torques, the angular difference between the orientation of thetransducer array and the measured rotational position of the drive motoris a constant times the applied torque. Thus, the system processor canestimate transducer rotational orientation by implementing an algorithmthat computes the drive motor's measure rotational position plus acorrection constant multiplied times the applied torque (which will bepositive or negative depending upon the direction in which torque isapplied). This correction constant can be estimated based upon thematerial properties and length of the drive wire 36 or drive line 361,362, or may be measured during design and development.

In an alternative embodiment, a constant speed motor may be used insteadof a stepper motor, with ultrasound image frames obtained periodicallythroughout the rotational scan. By measuring the drive motor'sorientation at the time each ultrasound image is obtained, the systemprocessor can estimate the orientation of the transducer array at thetime of the image using methods similar to that illustrated in FIG. 15.When ultrasound image frames are obtained while the transducer array isrotating, the resulting images will be inclined with respect to thedirection of rotation in an amount proportional to the rotation rate(i.e., degrees per unit time). This small imaging error may beacceptable and may be processed out by the imaging system processor.Such a system may exhibit nonlinear transducer-to-drive motor rotationaldifferences toward the maximum rotational angles as the drive motorstops and reverses direction and the transducer array follows suit. Toavoid increased imaging errors, and simplify the transducer orientationestimating procedure, the system processor can be programmed to simplynot image or ignore images obtained near the rotation angle limits,taking/storing images in the center of the rotation sweep where thetransducer orientation is more predictable.

In embodiments using drive lines 361, 362, additional compensation maybe required to account for differences in the drive line lengths causedby bending of the catheter body. For example, a ninety-degree bend overa one inch radius of a nine French catheter results in a difference of 4millimeters between opposite sides of the interior of the catheter.Thus, if the drive lines are on opposite sides of the catheter, bendingof the catheter will cause the transducer array to turn slightly. Thiseffect can be reduced by passing the drive lines 361, 362 side by sidein the catheter. A correction factor can be determined by the systemprocessor based upon measuring the steering controller position andapplying a correction factor based upon the measured position.

Using the foregoing methods, the system processor can thus estimate therotational orientation of the phased array transducer with respect toits imaging centerline or the window portion 33 of the catheter at eachinstant, and particularly when each ultrasound image frame is obtained.In operation, the system processor can control the processes of rotatingthe phased array transducer (via commands to the step motor controller)and generating ultrasound images (via commands to the beam formercircuits) so that ultrasound images are obtained when the transducerarray is stopped at a particular rotational orientation (versus duringmovement). Also, the system processor can record the estimatedrotational orientation of the transducer with each generated ultrasoundimage frame, so each image is correlated to the transducer rotationalorientation at the time the image was obtained. By correlating imageframes with the transducer orientation at the time each image wasobtained, the system processor generates and stores information that canbe used to construct three-dimensional images by merging, combining orotherwise processing the data. As with other functions performed by thesystem processor, the processor is adapted and configured to perform thefunctions via software operating in the processor. Additionally, theprocessor can be configured with electrical connections (e.g., standardinput/output ports and data cables) for transmitting commands to thestepper motor controller (or other type of motor controller) and theultrasound beam former circuits, and receiving signals from the steppermotor controller (e.g., related to motor orientation and applied torque)and ultrasound data signals from the beam former circuits.

The various embodiments of the ultrasound imaging catheter may beassembled using methods similar to those used to assemble conventionalultrasound imaging catheters, with the additional consideration that therotational elements of the ultrasound imaging assembly 3 need to bephysically aligned and seated within the catheter body 10. The distalportion of the catheter body 10, including the acoustic window portion33, may be fabricated as separate parts that are joined to the catheterbody 10 during assembly of the catheter system 1. This option mayfacilitate assembly because any seating or limiting structures (e.g.,bearing seat 350 and lip 350A) that mate or contact rotating elements ofthe ultrasound imaging assembly 3 can be provided in a relatively shortseparate part while the majority of the catheter body 10 comprises asmooth bore elongated tube. In this configuration, the internal elementsof the catheter system 1 can be fed through the main catheter body tube,and followed by seating and aligning of the moving parts to a shortdistal segment of the catheter which is then glued or otherwise bondedto the main catheter body tube. Further, there may be multiple shortdistal sections, such as a bearing seating portion and an acousticwindow portion 33, which are sequentially assembled over the internalelements and bonded to the rest of the catheter. Short sections may alsobe used to facilitate positioning centering discs 240 i and passing thedrive wire 36 and wire harness 13 through the discs. (This embodiment ofmultiple distal catheter segments is presumed in the assembly flowprocess illustrated in FIG. 16 for example purposes only.) For theembodiments in which the acoustic coupling fluid is added at the time ofmanufacture, once all components are assembled and proper rotationaloperations confirmed, acoustic coupling fluid can be added to the fluidfilled gap 32 and the distal cap 211 can be glued or otherwise bonded tothe open end of the short distal segment of the catheter. For theembodiments in which the clinician adds acoustic coupling fluid at thetime of use or sterile saline is flowed through the catheter during use,a shipping/storage cap can be applied after proper rotation operationsare confirmed.

Referring to FIG. 16, the various internal elements of the catheter(i.e., those parts that fit within the catheter body 10) are firstassembled, step 1601, and quality checked to ensure all electrical andmechanical connections are properly made, step 1602. The wire harness 13and steering wires 11, 12 may be connected to the handle assembly 2 atthis time or later (e.g., after assembly of the catheter 1), step 1612.The internal elements are then fitted into an assembly sleeve or otherassembly jig, step 1603, and threaded into the main catheter body andthe assembly sleeve removed, step 1604. In embodiments using separatedistal catheter portions, the moving parts of the ultrasound imagingassembly 3 will now be extending from the distal end of the maincatheter body. Next, the distal portion of the catheter containingseating, positioning and sealing structures (such as bearing seats andgrooves) is fitted over the ultrasound imaging assembly 3 so thatseating surfaces are properly aligned and mated to the correspondingstructures (e.g., bearings 35, 365 and a divider disc 240, dependingupon the particular embodiment), step 1605. At this point, the properrotational operation of the ultrasound imaging assembly 3 moving partsmay be confirmed, and alignments adjusted as necessary, step 1606.

Once proper alignment and rotational operation are confirmed, the distalportion of the catheter can be bonded to main catheter body, step 1 607.It is worth noting that the steps of bonding catheter segments togethercan be performed later after all parts have been assembled. Next, theacoustic window portion 33 can be positioned over the transducer array31, step 1608, and the alignment checked to confirm the array does notcontact the interior surface of the window portion during rotation, step1609. This step may involve engaging a bearing seat 350 with theproximal bearing 35 if the bearing seat is provided in the windowportion. If a distal bearing 37 is used in the implemented embodiment,this bearing can be positioned on the transducer array 31 as part ofthis step.

Once proper alignment of the acoustic window portion 33 and thetransducer array 31 and rotational operation are confirmed, the acousticcoupling fluid can be added and all bubbles removed, step 1610. Next,the distal end of the catheter can be sealed by positioning the distalcap 211 over the opening and bonding it to the acoustic window portion33, step 1611. Depending upon the design, this step may involve aligningand seating the distal bearing 37 on a bearing seat provided in thedistal cap 211. The catheter assembly may then be connected to thehandle assembly, connecting the wire harness 13 to a cable 21 andsteering wires 11, 12 and/or drive wires 361, 362 to the drivemechanisms in the handle (e.g., the deflection manipulator 22 and/ordrive motor 25), step 1612.

Now fully assembled, the catheter assembly can be given final qualitycontrol and functional checks, step 1613, and then cleaned, packaged andsterilized, step 1614. As noted above, the presence of the acousticcoupling fluid in the catheter in some embodiments may dictate the useof particular sterilizing methods, such as chemical cleaning prior topackaging followed by gamma radiation exposure within the sealedpackaging.

The foregoing steps may be performed in any order, and the illustratedand described order is but one possible sequence for assembling variousembodiments. For example, the steps of positioning the acoustic windowportion 33 and distal catheter portion over the moving parts of theultrasound imaging assembly 3, one or more of steps 1605-1611, may beperformed and quality confirmed before the rest of the catheterinternals are threaded into the main catheter body, step 1604.

Once assembled, tested and sterilized, the dynamic ultrasound imagingcatheter assembly can be packaged in a sterile package, such as aplastic bag that is thermally sealed on all edges to maintain thesterility of the catheter assembly, to form a medical diagnostic kit.This kit may further include a cable with connectors for electricallyconnecting the ultrasound imaging catheter assembly to a systemprocessor, a supply of acoustic coupling fluid to be inserted into thewindow portion, one or more filling tools to aid in filling the windowportion with acoustic coupling fluid, and instructions explaining thepreparation and use of the catheter.

Typical operation of the various embodiments of a dynamic ultrasoundimaging catheter is illustrated in FIG. 17. As with conventionalultrasound imaging catheters, the imaging portion (i.e., the distalportion containing the ultrasound imaging assembly 3) of the catheter isinserted into the subject via standard catheterization procedures, step1701. As part of this step, the catheter may be advanced with the tipportion deflected in order to thread the catheter into the veins orventricles of the heart. The location of the transducer array may thenbe determined, step 1702, using known procedures, such as fluoroscopy,and/or recently invented methods and devices disclosed in U.S. patentapplication Ser. No. 11/610,357 entitled “Catheter Position Tracking forIntracardiac Catheters” and Ser. No. 11/610,386 entitled “CatheterPosition Tracking Methods Using Fluoroscopy and Rotation Sensors,”previously incorporated by reference. As explained in those patentapplications, determining the location and orientation of the transducerarray is important to be able to assemble a series of ultrasound imagesinto a composite, such as a composite three-dimensional image. With thecatheter positioned in the patient's organ (e.g., the heart), theclinician may obtain and view ultrasound images to confirm that thecatheter is properly positioned to image the portion of the organdesired, step 1703. In this step, the clinician may view the liveultrasound image to see what part of the organ is imaged. If theclinician determines that the transducer is in an incorrect position ororientation, the steps 1701-1703 of position and confirming the locationof the catheter and viewing live images may be repeated until thedesired viewing perspective is achieve. Next, the clinician may scan thetransducer array through its viewing angle (i.e., rotation angle) whileviewing the live ultrasound image to confirm that the image volumeencompasses the portion of the organ to be imaged, step 1704. Theclinician may do this by pressing a button 23, 24 on the handle assembly2 while viewing the ultrasound system display. By pressing one or bothbuttons, or selecting a menu option on the ultrasound control system,the clinician can direct the system to rotate the transducer array asingle angular increment at a time or continually scan back and forththrough the scanning angle. If the clinician is dissatisfied with theimaging volume, he or she may rotate the catheter assembly by twistingthe handle, thereby adjusting the rotational orientation of the catheter(and thus the orientation of the imaging volume), and then repeat steps1703 and 1704 of confirming that the imaging volume encompasses thedesired volume of the organ being imaged.

Once the clinician has confirmed proper position of the transducer arrayto image the desired volume, the clinician can then begin ultrasoundimaging while scanning (oscillating) the transducer array back and forththrough the scanning angle by pressing one or two buttons 23, 24 on thehandle assembly 2, step 1705. In this step, the ultrasound systemautomatically rotates the transducer array back and forth through thescanning angle while obtaining and storing ultrasound images. Ultrasoundimages are stored in memory within the ultrasound system along with dataindicating the transducer array angle of rotation and time of eachimage. Once sufficient images have been obtained, the clinician mayreposition the catheter to image a different volume of the patient instep 1707 by more or less repeating steps 1701-1706. The imaging sessionis terminated in the same manner as conventional catheterizationprocedures. Finally, the stored images can be reviewed, processed andcombined using the ultrasound system or other image processing systems,step 1708. This processing may include stitching together a series ofimages to produce composite three-dimensional images.

By automatically rotating the transducer array, the ultrasound cathetercan generate the image data necessary to create three-dimensionalcomposite images without requiring the clinician to rotate the catheteror otherwise manage the scanning motion. By repeatedly and accuratelyrotating the catheter through the scanning angle, many images can beobtained across the angle of rotation without increasing the workload ofthe clinician.

The various embodiments provide an imaging ultrasound transducer arrayassembly that can scan through a range of viewing angles, such as 30, 60or 90 degrees about the longitudinal axis. The transducer array providesa planar image spanning typically about 90 degrees parallel to thelongitudinal. Thus, the various embodiments can provide ultrasound imagedata encompassing a volume spanning about 90 degrees parallel to thetransducer array long axis and about 30, 60 or 90 degrees perpendicularto the transducer array long axis. Additionally, by noting thetransducer rotational orientation and time associated with each planarimage, the ultrasound imaging data can be saved in the ultrasound systemfor subsequent processing into three-dimensional and four-dimensional(including time) composite images encompassing the imaged volume.

There are several benefits to providing a controlled axial oscillatingrotation capability. For instance, the present invention will enablegeneration of three-dimensional axial views of tissue even when the tipof the catheter is in a deflected (i.e., bent) configuration. This isachievable because the transducer array turns within the catheter,instead of rotating the whole catheter body.

The various embodiments also simplify some of the tasks that a physicianmust perform during imaging procedures. The instant invention allows thephysician to smoothly rotate the imaging transducer array within acatheter by simply pressing a button on the handle assembly oractivating a control on the ultrasound system, thereby obviating theneed to rotate the handle by twisting the wrist or arm to turn thecatheter along its axis. By controlling the transducer arrayrotation/orientation using the stepper motor, the potential for injuryto the patient from movement of the catheter body is eliminated.

While the present invention has been disclosed with reference to certainexemplary embodiments, numerous modifications, alterations, and changesto the described embodiments are possible without departing from thesphere and scope of the present invention, as defined in the appendedclaims. Accordingly, it is intended that the present invention not belimited to the described embodiments, but that it have the full scopedefined by the language of the following claims, and equivalentsthereof.

1. An ultrasound imaging catheter, comprising: a catheter body havingproximal and distal ends and a diameter limited in size to less thanabout 10 French (3.3 mm); an acoustic window portion coupled to thedistal end of the catheter body, the acoustic window portion having aninterior surface; a phased array ultrasound transducer housed within theacoustic window portion, the phased array transducer comprising a longaxis and configured so that a gap exists between the phased arrayultrasound transducer and the interior surface of the acoustic window;an acoustic coupling fluid filling the gap between the transducer arrayand the interior surface of the acoustic window; and a rotor portion ofan electric drive motor positioned within a sealed thin walled portionof the proximal end of the catheter body and mechanically configured andcoupled to the phased array ultrasound transducer so as to rotate thephased array ultrasound transducer about a long axis of the distal endof the catheter body, wherein the sealed thin walled portion of theproximal end of the catheter body is configured to removably slip intoan opening of a separate reusable structure, wherein the opening isconfigured within a reusable stator portion of the electric drive motorpositioned within the reusable structure.
 2. The ultrasound imagingcatheter of claim 1, further comprising a drive wire mechanicallycoupling the rotor portion of the electric drive motor to the phasedarray ultrasound transducer, wherein the drive wire is configured totransmit torque from the drive motor to the phased array ultrasoundtransducer.
 3. The ultrasound imaging catheter of claim 1, furthercomprising: a first drive spool coupled to the rotor portion of theelectric drive motor; a second drive spool coupled to the phased arrayultrasound transducer; and two tension lines coupled to the first andsecond drive spools, wherein the first and second drive spools and twotension lines are configured to transmit a rotational force from thedrive motor to the phased array ultrasound transducer for rotating thephased array ultrasound transducer about the long axis of the distal endof the catheter body.
 4. The ultrasound imaging catheter of claim 1,further comprising a removable cap coupled to a distal end of theacoustic window portion, wherein the ultrasound imaging catheter isconfigured so the acoustic coupling fluid can be added to fill the gapbetween the phased array ultrasound transducer and the interior surfaceof the acoustic window at the time of use.
 5. The ultrasound imagingcatheter of claim 1, further comprising: a removable cap coupled to adistal end of the acoustic window portion; and a saline injection portcoupled to the proximal end of the catheter body, wherein the ultrasoundimaging catheter is configured so a stream of acoustic coupling fluidcan be injected via the saline injection port and exit via the distalend of the acoustic window portion during use, thereby filling the gapbetween the phased array ultrasound transducer and the interior surfaceof the acoustic window when in use.
 6. The ultrasound imaging catheterof claim 1, further comprising a first bearing located near a proximalend of the acoustic window portion and coupled between the catheter bodyand a proximal end of the phased array ultrasound transducer.
 7. Theultrasound imaging catheter of claim 6, further comprising a secondbearing located near a distal end of the acoustic window portion andcoupled between the inner surface of the acoustic window portion and adistal end of the phased array ultrasound transducer.
 8. The ultrasoundimaging catheter of claim 1, further comprising a flexible fluid sealcoupled between the inside surface of the acoustic window portion andthe phased array ultrasound transducer.
 9. The ultrasound imagingcatheter of claim 2, further comprising a plurality of centering discspositioned within and along a length of the catheter body.
 10. Theultrasound imaging catheter of claim 1, further comprising a gearcoupled between the rotor portion of the electric drive motor and thephased array ultrasound transducer.
 11. The ultrasound imaging catheterof claim 10, further comprising a rotation sensor configured to sense arotational orientation of the drive motor and provide a signal to asystem processor indicative of the rotational orientation of the drivemotor.
 12. The ultrasound imaging catheter of claim 3, wherein at leastone of the first and second drive spools comprises two spiral grooves inits exterior with one of the two tension lines winding into one of thetwo spiral grooves and the other of the two tension lines winding intothe other of the two spiral grooves.
 13. An ultrasound catheter imagingsystem, comprising: a processor; a reusable structure comprising areusable stator portion of an electric drive motor; and an ultrasoundimaging catheter configured to be electrically coupled to the processorthrough the reusable structure, the ultrasound imaging cathetercomprising: a catheter body having proximal and distal ends and adiameter limited in size to less than about 10 French (3.3 mm); anacoustic window portion coupled to the distal end of the catheter body,the acoustic window portion having an interior surface; a phased arrayultrasound transducer housed within the acoustic window portion, thephased array transducer comprising a long axis and configured so that agap exists between the phased array ultrasound transducer and theinterior surface of the acoustic window; an acoustic coupling fluidfilling the gap between the transducer array and the interior surface ofthe acoustic window; and a rotor portion of the electric drive motormechanically positioned within a sealed thin walled portion of theproximal end of the catheter body and configured and coupled to thephased array ultrasound transducer so as to rotate the phased arrayultrasound transducer about its long axis, wherein the sealed thinwalled portion of the proximal end of the catheter body is configured toremovably slip into an opening of the reusable structure, wherein theopening is configured within the reusable stator portion of the electricdrive motor positioned within the reusable structure, wherein theprocessor is adapted and configured to: determine a rotationalorientation of the phased array ultrasound transducer at a time whenultrasound data is generated by the phased array ultrasound transducer;receive the ultrasound data from the phased array ultrasound transducer;generate an ultrasound image using the received ultrasound data; andcorrelate the generated ultrasound image with the determined rotationalorientation of the phased array ultrasound transducer at the time whenthe ultrasound data was received from the phased array ultrasoundtransducer.
 14. The ultrasound catheter imaging system of claim 13,further comprising a drive wire mechanically coupling the rotor portionof the electric drive motor to the phased array ultrasound transducer,wherein the drive wire is configured to transmit rotational force fromthe electric drive motor to the phased array ultrasound transducer forrotating the phased array ultrasound transducer about a long axis of thedistal end of the catheter body.
 15. An ultrasound catheter imagingsystem comprising: a processor; and an ultrasound imaging catheterconfigured to be electrically coupled to the processor, the ultrasoundimaging catheter comprising: a catheter body having proximal and distalends; an acoustic window portion coupled to the distal end of thecatheter body, the acoustic window portion having an interior surface; aphased array ultrasound transducer housed within the acoustic windowportion and configured so that a gap exists between the phased arrayultrasound transducer and the interior surface of the acoustic window;an acoustic coupling fluid filling the gap between the transducer arrayand the interior surface of the acoustic window; a drive motormechanically positioned near the proximal end of the catheter body; afirst drive spool coupled to the drive motor; a second drive spoolcoupled to the phased array ultrasound transducer; and two tension linescoupled to the first and second drive spools, wherein the first andsecond drive spools and two tension lines are configured to transmit arotational force from the drive motor to the phased array ultrasoundtransducer for rotating the phased array ultrasound transducer about along axis of the distal end of the catheter body, wherein the processoris adapted and configured to: determine a rotational orientation of thephased array ultrasound transducer at a time when ultrasound data isgenerated by the phased array ultrasound transducer; receive theultrasound data from the phased array ultrasound transducer; generate anultrasound image using the received ultrasound data; and correlate thegenerated ultrasound image with the determined rotational orientation ofthe phased array ultrasound transducer at the time when the ultrasounddata was received from the phased array ultrasound transducer.
 16. Theultrasound catheter imaging system of claim 13, wherein the processor isfurther adapted and configured to control the drive motor.
 17. Theultrasound catheter imaging system of claim 13, wherein the processor ispositioned within ultrasound system equipment.
 18. A medical diagnostickit comprising: a sterile package; and an ultrasound imaging cathetercontained within the sterile package, the ultrasound imaging cathetercomprising: a catheter body having a longitudinal axis, proximal anddistal ends, and a diameter limited in size to less than about 10 French(3.3 mm); an acoustic window portion coupled to the distal end of thecatheter body, the acoustic window portion having an interior surface; aphased array ultrasound transducer housed within the acoustic windowportion, the phased array transducer comprising a long axis andconfigured so that a gap exists between the phased array ultrasoundtransducer and the interior surface of the acoustic window; and a rotorportion of an electric drive motor positioned within a sealed thinwalled portion of the proximal end of the catheter body and mechanicallyconfigured and coupled to the phased array ultrasound transducer so asto rotate the phased array ultrasound transducer about its long axis,wherein the sealed thin walled portion of the proximal end of thecatheter body is configured to removably slip into an opening of aseparate reusable structure, wherein the opening is configured within areusable stator portion of the electric drive motor positioned withinthe reusable structure.
 19. The medical diagnostic kit according toclaim 18, further comprising a supply of an acoustic coupling fluid forfilling the gap between the transducer array and the interior surface ofthe acoustic window.
 20. The medical diagnostic kit according to claim18, further comprising a filling tool to assist in filling the gapbetween the transducer array and the interior surface of the acousticwindow with an acoustic coupling fluid.
 21. An ultrasound imagingcatheter, comprising: a catheter body having proximal and distal endsand a diameter limited in size to less than about 10 French (3.3 mm); anacoustic window portion coupled to the distal end of the catheter body,the acoustic window portion having an interior surface; a phased arrayultrasound transducer housed within the acoustic window portioncomprising a long axis and configured so that a gap exists between thephased array ultrasound transducer and the interior surface of theacoustic window; an acoustic coupling fluid filling the gap between thetransducer array and the interior surface of the acoustic window; adrive motor positioned near the proximal end of the catheter body; afirst drive spool coupled to the drive motor; a second drive spoolcoupled to the phased array ultrasound transducer; and two tension linescoupled to the first and second drive spools, wherein the first andsecond drive spools and two tension lines are configured to transmit arotational force from the drive motor to the phased array ultrasoundtransducer for rotating the phased array ultrasound transducer about along axis of the distal end of the catheter body.
 22. The ultrasoundimaging catheter of claim 21, further comprising a removable cap coupledto a distal end of the acoustic window portion, wherein the ultrasoundimaging catheter is configured so the acoustic coupling fluid can beadded to fill the gap between the phased array ultrasound transducer andthe interior surface of the acoustic window at the time of use.
 23. Theultrasound imaging catheter of claim 21, further comprising: a removablecap coupled to a distal end of the acoustic window portion; and a salineinjection port coupled to the proximal end of the catheter body, whereinthe ultrasound imaging catheter is configured so a stream of acousticcoupling fluid can be injected via the saline injection port and exitvia the distal end of the acoustic window portion during use, therebyfilling the gap between the phased array ultrasound transducer and theinterior surface of the acoustic window when in use.
 24. The ultrasoundimaging catheter of claim 21, further comprising a first bearing locatednear a proximal end of the acoustic window portion and coupled betweenthe catheter body and a proximal end of the phased array ultrasoundtransducer.
 25. The ultrasound imaging catheter of claim 24, furthercomprising a second bearing located near a distal end of the acousticwindow portion and coupled between the inner surface of the acousticwindow portion and a distal end of the phased array ultrasoundtransducer.
 26. The ultrasound imaging catheter of claim 21, furthercomprising a flexible fluid seal coupled between the inside surface ofthe acoustic window portion and the phased array ultrasound transducer.27. The ultrasound imaging catheter of claim 22, further comprising aplurality of centering discs positioned within and along a length of thecatheter body.
 28. The ultrasound imaging catheter of claim 21, furthercomprising a gear coupled between the drive motor and the phased arrayultrasound transducer.
 29. The ultrasound imaging catheter of claim 28,further comprising a rotation sensor configured to sense a rotationalorientation of the drive motor and provide a signal to a systemprocessor indicative of the rotational orientation of the drive motor.30. The ultrasound imaging catheter of claim 21, wherein at least one ofthe first and second drive spools comprises two spiral grooves in itsexterior with one of the two tension lines winding into one of the twospiral grooves and the other of the two tension lines winding into theother of the two spiral grooves.